FIG. 4 is a plan view showing commonly used pixels on a TFT substrate for use in liquid crystal displays that is manufactured by using thin-film transistors of the field-effect type.
Signal lines 21 and gate lines 22 are installed on an insulating substrate so as to orthogonally intersect each other, and a thin-film transistor 20 having a source electrode 20a, a drain electrode 20b and a gate electrode 20c is placed in the vicinity of each of the intersections of the signal lines 21 and the gate lines 22. The source electrode 20a is connected to the corresponding signal line 21, the gate electrode 20c is connected to the corresponding gate line 22, and the drain electrode 20b is connected to the corresponding pixel electrode 23. Here, in FIG. 4, the reference numeral 24 represents a pixel storage capacitance.
The thin-film transistor 20 is a thin-film transistor of the so-called reversed stagger type wherein the gate electrode is placed right above the insulating substrate. Referring to FIGS. 5(a) and 5(b), an explanation will be given of a manufacturing method of a conventional thin-film transistor of the reversed stagger type. Here, FIG. 5(a) is a plan view of a thin-film transistor of the reversed stagger type that was manufactured in a conventional method, and FIG. 5(b) is a cross-sectional view taken along line V--V of FIG. 5(a).
First, a gate-electrode material layer is formed on an electrically insulating substrate 32, and the gate-electrode material layer is patterned into a predetermined shape by a photolithography technique consisting of coating of photoresist, a patterning process of the resist (consisting of an exposing process and a rinsing process), an etching process, a removing process of the resist, etc.; thus, gate electrodes 33 are formed. Next, the surfaces of the gate electrodes 33 are subjected to anodic oxidation so that a gate insulating film 34 is formed, and then a gate insulating film 35 is formed in a manner so as to cover the gate electrodes 33. Additionally, the gate insulating films 34 and 35 are omitted from FIG. 5(a).
Next, a semiconductor-material layer that subsequently serves as a semiconductor layer 36 and a contact-material layer 37 that subsequently serves as contact layers 37a and 37b are formed in this order, and the semiconductor-material layer and the contact-material layer 37 are patterned at the same time by the photolithography technique. In this case, since only the semiconductor layer 36 is first patterned, the pattern of a gap section 40 between the source electrode 38 and the drain electrode 39 has not yet been formed. Successively, the pattern of the gap section 40 is formed in the contact material layer 37 by the photolithography technique so that the contact layers 37a and 37b are formed (in FIG. 5(a), the contact layers 37a and 37b are indicated by cross-hatched regions). Here, there is a generally known manufacturing process in which at this time, an etching stopper layer is provided in the region of the gap section 40 between the semiconductor-material layer and the contact-material layer 37.
Thereafter, an electrode material that subsequently serves as a source electrode 38 and a drain electrode 39 is formed, and this electrode material is patterned by the photolithography technique so that source electrode 38 and the train electrode 39 are formed. The thin-film transistor of the reversed stagger type is manufactured by the processes as described above.
In this manner, the above-mentioned manufacturing method inevitably needs to use a specific resist pattern in order to form the gap section 40 during a patterning process of the gap section 40. This is also required in other conventional manufacturing methods similar to the above-mentioned manufacturing method.
In the current manufacturing processes of thin-film transistors, reduction of the number of processes has been a major problem to be solved in order to reduce the production costs and to improve the yield of desired products. However, in the above-mentioned conventional manufacturing methods, the production of the resist pattern used for the formation of the gap section further requires photolithography processes such as coating of resist and patterning of the resist (an exposing process and a rinsing process), resulting in a further problem of numerous processes.